Fluorouracil (5FU) 0.5% cream or ointment (Carac® Efudex®, Fluoroplex®) is a prescription fluoropyrimidine used in some types of skin cancer, such as basal cell carcinoma, and actinic keratosis (AK). Approved by the US Food and Drug Administration in October 2000, 5-FU works by affecting DNA and RNA synthesis and inducing cell cycle arrest and cell death – or apoptosis – in cells with an abnormal growth rate such as cancer cells.

Treatment with 5-FU can vary, depending on the degree of the problem, but typically the ointment is applied twice a day for several weeks. This application provides several advantages in that it can be used to treat areas of skin cancer or AK that would be too large to remove surgically, and it doesn’t leave scarring, which can occur in the treatment of AK. If you’re using 5-FU topical ointment, it’s advisable to avoid sunlight or other ultraviolet light sources such as tanning beds. If you’re going to be out in the sun while you’re on treatment, use appropriate sun protection such as long-sleeved shirts, full length pants and hats.

The 0.5% 5-FU cream carries an FDA pregnancy category risk of X, which means it is contraindicated in women who are or may become pregnant. The 0.5% cream is also contraindicated in people with dihydropyrimidine dehydrogenase (DPD) enzyme deficiency, and in anyone who has a known hypersensitivity to any of the components of the cream. The most common adverse effect is facial irritation. Reddening, blistering or peeling may also occur 1-2 weeks after starting treatment.